A ferrite for magnetostrictrive vibrators is produced by the simple process of press forming a preformed structure formed from starting powder of magnetite or a mixture of magnetite and ferric oxide, said powder having an average particle size d (.mu.) of from 0.02 to 5.0 .mu., sintering this structure in an atmosphere wherein the partial pressure of oxygen is from 10.sup.-1 to 10.sup.-11 atmosphere at a temperature of from 1,000.degree. to 1,350.degree. C. and which will meet the requirement: and thereafter cooling the structure thus sintered to room temperature at a cooling rate m (.degree.C./min.) <0.5f where f(KHz) is a corresponding resonance frequency thereby to produce a macroscopically homogeneous ferrite structure containing as its principal constituent a sintered magnetite having an oxygen/iron (O/Fe) atomic ratio of 4.0/3<0/Fe<4.1/3, and a density of at least 90% of the theoretical density.
The drive modules of a magnetostrictive transducer are fabricated from interleaved permanent magnet disks (samarium cobalt) and high-strain, low-permeability magnetostrictive lanthanide alloy (Terfenol-D) disks to form a stack of such interleaved materials of substantially uniform magnetic field distribution in the stack. Two such stacks in side-by-side relationship provide a series-aiding magnetic circuit completed through high-permeability flux return pole pieces at their ends thereby providing a substantially uniform magnetic field distribution in the stack. Each stack has longitudinally-extending and electrically-insulated planar cuts and each flux return pole piece is a laminate of thin sheets of high-permeability electrically-insulated steel to reduce eddy current losses resulting from the AC field. The steel sheets are constrained by a nonmagnetic end-block into which the steel sheets are inserted and bonded.
Disclosed herein is a composite permanent magnet and a circuit which employs a plurality of such magnets. The composite magnet combines discrete sections of a first magnet material with at least one discrete section of a second magnetic material. The first material has a high residual magnetic strength and a moderate energy product. The second material is many times more expensive than the first material and is characterized by a high residual magnetic strength and a high energy product. Also disclosed is a circuit combining a plurality of such composite magnets. The circuit combines the above magnets in such a way that there is a reduction in magnetic leakage in the circuit.
The present invention provides magnetostrictive compositions that include an oxide ferrite which provides mechanical properties that make the magnetostrictive compositions effective for use as sensors and actuators.
The present invention provides magnetostrictive composites that include an oxide ferrite and metallic binders which provides mechanical properties that make the magnetostrictive compositions effective for use as sensors and actuators.
